Electrodeposition of metals and bath composition therefor



' troplating baths but ing upon the composition Patented Aug J20, 1946 ELECTBODEPOSITION F .METALS AND BATH COMPOSITION THEREFOR Kenneth M. Gaver, Columbus, Ohio, assignor, by

v a corporation of Ohio No Drawing. Application February 15, 1941,

, Serial No. 879,127

This invention relates to electro-deposition of metals, and more particularly to electroplating baths containing a salt or the metal to be deposited and an addition agent for producing a bright adherent plate on the base metal.

It is an object of this invention to provide an improved electroplating bath for producing bright, smooth, uniform metal coatings in electroplating processes.

Another object is to provide an improved electroplating bath composition which comprises a colloidal solution of an amylaceous compound which is incorporated in sufllcient amount to inhibit the building up of large crystals of metal during the electrodeposition so as to form a metal deposit having an adherent coating of high luster. These and other obiects and advantages will be apparent from the following description.

My invention nickel plating, but, in its broadest aspects, is applicableas an improved plating bath for producing a smooth, uniform plate in electrodepositing other metals, such as chromium, copper, zinc, cadmium, cobalt and iron. In this connection, it has been proposed heretofore to use colloidal solutions as addition agents in nickel plating baths as brighteners but they have not been employed to a great extent bee cause of the diiilculty of controlling their eifect and, in general, are restricted to use in low current density operations. A wide variety of organic and inorganic compounds has been suggested heretofore as addition agents in elecnone of these materials has been entirely successful.

According to the present invention, there is employed a metallic starchate compound which incorporates both the metal ion and starch molecule. The particular starchate compound may be selected to correspond to the metal-salt which is in solution in the bath for supplying the metal to be deposited. The amount of the addition agent added may vary widely dependof the electroplating bath, and the control or addition agent may be incorporated in the form of a powder, or preferably an aqueous solution.

My improved addition agent is produced by reacting starch with alcohol soluble hydroxides, such as sodium, potassium, and the like, under conditions such that the metallic starch alcoholate is produced wherein the alkali metal is attached through an oxygen atom to a carbon atom in the complex a-glucopyranose or a-glyis particularly adapted to assignments, to The Ohio State University Research Foundation, Columbus,

Ohio,

copyranose residue. This alkali metal starch alcoholate compound, which is referred to as a metallic starchate, when dissolved in water forms a limpid solution and may be incorporated as such in an electroplating bath.

The method of making the alkali metal starchatewhich is used in compounding my improved electroplating baths may consist of reacting 4 17 pounds of flake caustic soda or caustic potash in approximately 500 gallons of industrial ethyl alcohol. The mixture is allowed to stand to precipitate the carbonate impurities present which are removed by filtration.

Approximately 500 pounds of dry starch (i. e. potato starch) is introduced into the alcoholic NaOH solution and the whole mixture refluxed for two hours below 98 degrees C. while being vigorously stirred. The product is then filtered and washed free of alkali with ethyl alcohol and the filterproduct consisting of sodium starchate'is dried in a vacuum oven under '78 degrees C. equipped with means for preventing entry of carbon dioxide and means for recovery oi the alcohol. The dry product is then ground, screened and packed in substantially airtight containers.

The sodium starchate compound formed as described is readily soluble in water with spontaneous hydrolysis, whereas the original starch is insoluble.

In producing the sodium starchate, other sources of starch may be employed such as that derived from corn, wheat, rowroot, cassava, etc.

Further details regarding the manufacture of alkali metal starchates and derivatives thereof, their nature, and characteristics, are given in my copending application Serial No. 357,995, filed September 23, 1940.

Where it is desired to employ nickel starchate, this can be formed by reacting sodium starchate with nickel chloride in alcohol forming nickel chloro starchate. This compound may be used, or its amino derivative. The latter is made by reacting the nickel chloro starchate compound with ammonium hydroxide, filtering, and air drying the product to produce amino hydroxy starchate. If the amino hydroxy starchate is, dried at a higher temperature nickel hydroxy they may be readily made by reacting the alkali potatoes, sago, ar-

I quired.

metal starchates, such as sodium starchate, with the proper metal salt compound. I

. The following typical examples ll further illustrate my invention, but it is understood that my invention is'not limited to these particular baths, but is applicable to the preparation of various other metal plating baths depending upo the metal to be deposited.

- Example I p Parts by weight Nickel sulfate; -L 135-165 Nickel chloride 20-30 Boric a 20-40 Sodium starchate -25 The above ingredients are'dissolved in sufficient water, to provide an electrolytic. bath and the pH adjusted to the desired value by adding small amounts of sulphuric acid or alkali as re- Ercample II 'Parts by weight Nickel sulfate; 135-165 Nickel chloride, 20-30 Boric acid 20-40 Nickel starchate 5-25 Potassium starchate vided a novel addition agent for electroplating baths which may be used to introduce both the metal ion which is deposited from a solution and the amylaceous colloid for controlling the metal may be employed as addition agents in the electroplating baths are the following:

Sodium starchate Zinc starchate Tin starchate Cadmium starchate Cobalt starchate Nickel starchate Copper starchate Chromium starchate Iron starchate Silver starchate Molybdenum starchate The metal starchates listed are merely illustrative of the most common metal compounds which may be used. Any soluble starchate compound may be employed. Further, when desired the chloro, nitro or hydroxy starchate compound of the appropriate metal can be utilized.

The above ingredients are dissolved in sufliv cient water to provide-an electrolytic bath as in Example I. Y

' I Example III Parts by weight Sodium cyanide -a 100-125 Cadmium hydroxide -50 Sodium sulfate -55 Sodium starchatev (dry) '10-25 .The above ingredients are readily soluble in water to form an electroplating bath. In place of the sodium starchate, cadmium starchate may be substituted similarly as in Example 11.

Sodium starchate aqueous solution) 5-20 The above ingredients are mixed together and may be dissolved in approximately 100 gallons of water or in an amount to produce the desired pH value solution. Copper starchate may also be used in place of sodium starchate where desired.

The amount of metallic starchate agent added in practice may vary depending upon the acidity.

or alkalinity of the plating bath. Nickel and other similar metal plating solutions are readily affected by the addition of the starch colloidal solution and the amounts used, as well as other details of operation, it will be understood, are

regulated to produce tough, adherent, smooth coatings of the desired thickness.

In the foregoing examples,.it will be appreci- V ated that other metal salts and mixtures of different compounds may be used informulating the plating bath and the metallic starchate used alone or in conjunction with other modifying substances, such as sulphonated oils and the like. The metallic starchate addition agent combines the colloidal action of the starch molecule with the more reactive metal ion so as to perform the dual function of supplying an active metal ion and the colloidal dispersion properties of the starch molecule. In this manner, there is prothat it comprehends various plating baths reactions for forming the metal starchate product can be performed using water as asolvent, but where the product is to be used as a powder,

the drying of the finished product becomes an important factor. Adjustment of the addition agent, or agents, of course. will be made in the acid and alkali .electroplating baths in order to produce the improved results. 1

Further, my metallic starchate compound ma be conveniently supplied and stored as a dry powder wherein the consumer may dissolvethe dry powder ingredient in water and add it to the electroplating bath. Also, if desired. my addition agent may be incorporated in one or more of the ingredients forming the electroplating bath and during use, the remaining constituents of the bath incorporated and made up into a solution having the required pH value.

Alloys of various metals may also be electrodeposited from suitable combinations of salts with my addition agent made up in the proportion to produce a bright metal deposit. Alloys of nickel and iron or copper, as well as brass, may beacof the metal salts.

complished by using a mixture as is conventional in the art. With the use of large amounts of my starchate compound the viscosity of the electrolyte maybe increased somewhat over water and high current densities employed so that heavier deposits of metal may be formed.

It will be understood that my invention is adapted for widely different embodiments and which include metal starchate compounds as brightening agents and is not limited to the particular examples given, which are merely exemplary. It is also understood that the new addition agents may be incorporated in various amounts in the different baths as required to produce the improved results. l

Further, such modifications in the use of my a of starch and an alkali metal.

i new brightening agents as necessitated under different conditions and uses are contemplated 'to be within the scope ot'this invention.

ions of the metal to be deposited and a metal, starchate addition agent comprisingthe reaction product of starch and an alkali metal.

2. A plating bath for the electrodeposition of metal comprising an aqueous solution providing ions of the metal to be deposited and having a colloidal solution of a starchate compound comprising the reaction product of starch and an. alkali metal incorporated in said bath.

3. A plating bath for the electrodeposition of metal comprising an aqueous solution providing ions of the metal to be deposited and metal starchate in which the metal is attached in the 2-position in the starch molecule. as an addition agent. I

4. A plating bath for the electrodeposition of metal comprising an aqueous solution providing ions of the metal to be deposited and a colloidal solution of an alkali metal starchate in sufilcient amount to inhibit the building up of large crystals of metal during the deposition.

5. A plating bath for the electrode'position of metal comprising an aqueous solution providing ions of the metal to be deposited "by electrolysis and including as an addition agent for producing bright, smooth metal coatings an aqueous colloidal solution of metal starchate in which the metal is attached in the 2-position in the starch molecule. i

6. An electroplating bath comprising an aque ous solution providing ions of nickel to be deposited by electrolysis and a metal starchate compound in which the metal is that being deposited.

7. In a, process for the electrodeposition of metal, the step comprising depositing said metal from an aqueous electrolyte solution of a salt thereof in the presence of an addition agent con sisting of a metal starchate of the-metal being deposited.

8. In a process for the electrodeposition of metal, the step comprising depositing said metal from an aqueous electrolyte solution of a salt thereof in the presence of an alkali metal starchate compound comprising the reaction product 9. In a process of electrodeposition of metal. the step comprising depositing said metal from an aqueouselectrolytesolution oia salt thereof in-the presence of a colloidal aqueous suspension of a metal starchate compound in which the metal attached in the-2-position in the starch molecule.

10. A process for the electrodeposition 0! metal said electrolyte bath.

I which comprises passing electric current from an anode to a cathode through an aqueous electrolyte bath in the presence of a metal starchate compound in which the metal is attached in the 2-position in the starch molecule incorporated in 11. An electrolyte composition for use in electroplating metals, comprising an aqueous solution of an ionizable compound of the metal to' be deposited and as an addition agent a metal starchate of said metal being plated out.

12. An electrolyte for use in the electrodeposition of metal, comprising an aqueous solution of an ionizable compound -of the metal to be deposited andsumcient alkali metal starchate to produce a bright, adherent plate.

13. A plating bath comprising nickel sulfate, nickel chloride, boric cid, and sodium starchate dissolved in a sumcient quantity of water to provide a bath of the desired concentration.

14. A plating bath comprising by-welght nickel sulfate 135 to 165 parts, nickel chloride 20 to 30 parts, boric acid 20 to '20 parts, and sodium starchate 5 to 25 parts. r

15. A plating bath comprising nickel sulfate, nickel chloride, boric acid, nickel starchate, and

water in quantity sumcient to provide a bath of I the desired concentration.

' 16. A plating bath comprising by weight nickel sulfate 135 to 165 parts, nickel chloride 20 to 30 parts, boric acid 20 to 40 parts, and nickel starcha'te 5 to 25 parts.

17. A platingbath comprising sodium cyanide,

cadmium hydroxide, sodium sulfate, sodium starchate, and water in quantity sumcient to provide a 'bath of the desired concentration.

18. A plating bath comprising by wet sodium cyanide 100 to 125 parts, cadmium hydroxide 35 to 50 parts, sodium sulfate 40 to 55 parts, and

sodium starchate id to 25 parts, said um 'starchate content being based on the dry basis.

19'. A. plating bath comprising sodium cyanide, cadmium hydroxide, sodium sulfate, caum. starchate, and water in quantity sumcient to pro:-

vide a solution of the desired concentration.

20. A plating bath comprising by weight sodium cyanide its to 125 parts, cadmium hydroxide 35 to 50 parts, sodium sulfate 40 to parts. and cadmium starchate 10 to 25 parts. said cadmium starchate content being based on the dry basis.

21. A plating bath comprising copper cyanide.

sodium cyanide, sodium carbonate, sodium starchate, and water in quantity sufllcient to provide a bath of the desired concentration. I

22. A plating bath comprising by weight copper cyanide to parts, sodium cyanide to parts, sodium carbonate 25 to 30 parts, and sodium starchate 51:0 20 parts, said sodium starchate content being based on a 50% aqueous solution basis.

- KENNETH M. GAVER. 

